Does anyone know where to purchase good solar panels to use with a thermosiphoning DHW hot water system? Does thermosiphoning make sense for DHW in the northeast at the latitude of Long Island, NY. I set up a thermosiphoning system at this latitude and it has been working great in the summer but towards the end of August unless there is bright, hot sunny days the output falls off dramatically. In the northeast it may make sense as a supplement to an existing DHW from Thanksgiving to April 1st and then drain it during the winter.
Either a glycol or drain back might give you better output. Properly installed a water based drain back is the most efficient thermal solar system. Possibly use an ECM circ and keep the pumping cost to a minimum
is a pump with a high efficiency electronic motor. They consume 40- 60% less energy. think of like a more efficient light bulb.
Drainback does take some special design and installation care to provide a troublefree system. the pump & piping needs to be sized properly, and the piping needs to be installed to completely drainback.